Machines that are designed for cutting metal or steel do so by applying various tools to a workpiece. In various types of turning operations, this can be done by having a rotating tool approach a fixed workpiece or by spinning the workpiece itself (such as a piece of bar stock) as the tool comes in contact from a certain angle. The moving contact of the tool with the stock produces a large amount of heat which must be dissipated to avoid destroying the tool. Most cutting machines are equipped with a coolant reservoir and a low pressure pump that sprays coolant over the entire machining process from hoses with diameters as large as one inch. The purpose is to flood the entire cutting process which, in theory, improves the tool life by minimizing the temperature increase. This approach has several flaws, one of which is the fact that when machining certain high-temperature steels, the temperature is elevated high enough to literally burn away the coolant at the interface of the tool and the workpiece. Although it appears as if there is coolant covering the area of tool contact with the workpiece, there is actually a microscopic vapor pocket at the point of contact created by the intense heat. The described hoses are insufficient for this purpose. Increasing the coolant pump pressure, and reducing the size of the hose orifice, helps to reduce the heating, but at the cost of using much more coolant, and requires that the coolant hose be strongly secured to the machinery, to avoid the whipping fire hose effect action.
Relatively recently, machine tool manufacturers have increased the size and power of the pumps that are supplied with metal working machines. Within the last ten years, high pressure coolant pump systems, such as the type manufactured and sold by ChipBLASTER Ltd. have been used to deliver coolant at pressures in the range of 5000 psi at the cutting interface. The much higher pressure of the coolant requires customized fixtures to direct the coolant to the cutting interface.
One approach to direct pressurized coolant flow through the tool holder, to which the cutting tool is attached. For example, U.S. Pat. Nos. 4,695,208 and 4,955,264 disclose tool holders with coolant flow passageways through the body of the holder, with an exit port at the tool attachment point, or through a tool holder attachment insert. An inherent disadvantage of this approach is the complexity and cost of manufacturing the passageway through the tool holder. In the event the tool holder is damaged, as frequently happens in the event of a "crash" wherein the tool holder is driven too fast into the workpiece, the entire tool holder (with the coolant passage and coolant hose fitting) must be replaced. Another approach is to integrate the coolant passageway in a portion of a custom tool holder other than the attachment shank. This requires the tool holder to have extra mass, including an enlarged shank which requires larger clearances in machine set-ups. It also requires replacement of the entire tool holder in the event of damage, and is therefore a very expensive approach to cooling. Also, in these types of tool holders the orientation or angle of the coolant exit port is fixed relative to the cutting tool. In many applications, a particular fixed angle of coolant delivery may not provide adequate or optimized cooling action.